1. Field of the Invention
This invention generally relates to a friction member having a circular plate-like form with an aperture at its center, and is rotatable around its central axis. More specifically, the present invention relates to a friction disk that operates in a fluid chamber filled with fluid, such as a torque converter. Specifically, the friction disk is part of a disk assembly for transmitting a torque from an input rotary member to an output rotary member in a torque converter.
2. Background Information
In general, a torque converter transmits power via fluid, and therefore can facilitate smooth acceleration and deceleration. However, slinging of fluid results in energy losses and therefore low fuel efficiency.
A certain type of torque converter in the prior art is provided with a lock-up device for mechanically coupling a front cover on the input side to a turbine on the output side. The lock-up device is arranged in a space between the front cover and the turbine. The lock-up device is primarily formed of a circular plate-like piston, which can be pressed against the front cover, a driven plate, which is attached to a rear side of the turbine, and torsion springs for elastically coupling the piston and the driven plate together in the rotating direction. The piston has a circular and annular friction member which is fixed by adhesion to a portion of the piston opposed to the flat friction surface of the front cover.
In the conventional lock-up device, the operation of the piston is controlled by a working fluid or oil, which flows within a main unit of the torque converter. More specifically, the working fluid is supplied from an external hydraulic operation mechanism into a region between the piston and the front cover when the lock-up is released. This working fluid flows radially outward in the space between the front cover and the piston, and flows into the main unit of the torque converter through its radially outer portion. When the lock-up is engaged, the working fluid in the space between the front cover and the piston is drained through the radially inner side so that the piston moves toward the front cover. As a result, the friction member provided on the piston is pressed against the friction surface of the front cover. In this manner, a torque of the front cover is transmitted to the turbine side via the lock-up device.
In the conventional lock-up device, a multiple-disk clutch, which is provided with a plurality of friction plates for providing a plurality of friction surface is used for ensuring a sufficiently large torque transmission capacity.
A certain type of conventional lock-up device of the torque converter provided with the multiple-disk clutch may have, e.g., a clutch coupling portion, which includes a driven plate and drive plates arranged on the opposite sides thereof. The driven plate carries wet friction facings, which are fixedly coupled to its opposite sides for forming friction surfaces with respect to the respective drive plates. The clutch coupling portion of the multiple-disk type having such multiple friction surfaces may suffer from a problem relating to a drag torque. The drag torque is a torque which occurs due to contact between the drive and driven plates in the clutch released state.
The torque converter includes a front cover supplied with a torque of an engine, an impeller which is arranged on a transmission side with respect to the front cover for forming a fluid chamber together with the front cover, a turbine which is arranged in the fluid chamber and is opposed to the impeller to form a fluid operation chamber together with the impeller, a stator arranged radially inside the impeller and the turbine for regulating a flow of the fluid from the turbine to the impeller, and a power cut-off clutch which is arranged between the front cover and the turbine for transmitting and interrupting the torque from the turbine to the transmission.
The power cut-off clutch includes a pair of drive plates coupled to an engine, a piston for driving a pair of drive plates, a circular driven plate for rotation around a central axis, and a pair of friction facings fixedly coupled to axially opposite surfaces of the driven plate, respectively. The paired drive plates are coupled to the turbine, and can hold the driven plate and the paired friction facings from the axially opposite sides. The driven plate is coupled to the transmission.
The paired friction facings are made of circular plate-like members, each of which has a central aperture and is rotatable around the central axis. Each of the paired friction facings is provided on its surface, which is not fixedly coupled to the driven plate, with a plurality of grooves. As shown in FIG. 15, these plurality of grooves are formed of a plurality of grooves extending in a first direction parallel to a certain diametral direction and a plurality of grooves extending in a second direction perpendicular to the first direction.
When the torque converter operates, the fluid in the fluid chamber is moved radially outward by a centrifugal force. In this operation, the speed of the fluid flowing between the paired drive plates and the driven plate is lower than that of the fluid flowing between the front cover and the drive plate on the engine side. In particular, when the surfaces of the friction facings fixedly coupled to the axially opposite surfaces of the driven plate are parallel to the direction of the fluid flow, the fluid flows radially outward through the grooves provided on the contact surface.
When the engaged clutch is released, the fluid pressure on the transmission side of the piston lowers so that the piston and the drive plate neighbouring the piston are spaced from the other drive plate and the driven plate. In this operation, the speed of the fluid flowing between the paired drive plates and the driven plate is larger than the speed of the fluid flowing between the drive plate on the engine side and the front cover, and is also larger than the speed of the fluid flowing on the transmission side of the piston. Therefore, the pressure of the fluid flowing between the paired drive plates and the driven plate is low. As a result, the paired drive plates are pulled toward the driven plate so that the clutch cannot be released sufficiently, and a drag torque is transmitted to the transmission.
In view of the above, there exists a need for friction member which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.